1. Field of the Invention
The present invention relates to a combined blowing and suction system integrating exchange of energy between the two airflows.
2. Description of the Prior Art
Many operations performed on continuously moving strips, for example strips of paper, necessitate an input of energy. Drying is one such operation.
To preserve the quality of the surface state of the strip it is often indispensable for this input of energy to be without contact.
The techniques routinely used to dry a continuously moving strip without contact are:
convection drying using hot air; PA1 infrared drying using radiant burners. PA1 the efficiency of energy input by convection increases as the temperature of the blowing air increases, but PA1 the overall size of the drying installation increases as the temperature of the blowing air increases. PA1 reduces the temperature and/or the volume of blowing air at the inlet of the dryer because this air is heated before it impinges on the strip, and PA1 reduces the temperature and/or the volume of the air sucked out of the dryer because this air has exchanged energy with the blowing air.
Both these techniques must combine input of energy and of mass to perform the drying operation efficiently. In both cases blowing and suction means are employed.
Hot air dryers blow hot air onto the surface of the moving strip to transfer energy and mass at the same time. The blowing air charged with moisture is then evacuated via suction means.
Infrared dryers deliver energy in the form of radiation. Mass is transferred by blowing air parallel to the surface of the moving strip. The blowing air charged with moisture is then evacuated via suction means.
Both these technologies have to input maximum energy in the smallest possible space. These two imperatives are mutually incompatible because:
The object of the present invention is to propose a combined blowing and suction system which operates at a high blowing temperature but reduces the volume of the airflows.
In conventional hot air dryers the temperature of the sucked air charged with moisture is lower than the temperature of the blowing air. It is therefore necessary to prevent energy exchange between the two airflows because the energy input would otherwise be reduced.
In infrared dryers the temperature of the sucked moist air is higher than the temperature of the blowing air because the energy losses from the radiating elements heat the mixture of blowing air and water vapor produced by evaporation. It would therefore appear to be beneficial to transfer energy between the two airflows in order to reduce the temperature of the sucked air to the benefit of the temperature of the blowing air. However, the traditional arrangement of the blowing and suction means makes such exchanges difficult to implement.
The invention is based in particular on the combined convection/radiation system described in European patent application No. 98 402 768.0, which uses blowing and suction airflows and in which the temperature of the sucked airflow is higher than the temperature of the blowing airflow. The novel contiguous disposition of the blowing and suction means enables beneficial transfer of energy between the blowing and sucked airflows.